The present invention relates to a fuel cell in which liquid fuel is oxidized on the anode which is a component of a membrane electrode assembly (MEA) consisting of an electrode catalyst, anode, electrolyte membrane, cathode, and a diffusion layer, and then oxygen is reduced on the cathode.
In a conventional secondary cell, the cell must be charged after a constant amount of electric power has been used, which requires a charging device as well as a relatively long charging time. Accordingly, there are some problems in continuously operating mobile devices for a long period of time at any time and any place. In the future, mobile devices will require a power source which has high power density and high energy density, that is, a power source which can be continuously operated for a long period of time, in order to quickly process an increasing amount of information and achieve highly advanced functions. Thus, there are increasing needs for a compact power generator which does not need to be charged, that is, a micro power generator which can be easily supplied with fuel.
In the light of such circumstances, a fuel cell power source is considered to be a response to remedy the aforementioned request. The basic fuel cell at least consists of a solid or liquid electrolyte, two electrodes which induce desired electrochemical reaction, an anode, and a cathode. The fuel cell is a power generator which efficiently converts fuel's chemical energy directly into electrical energy by the action of an electrode catalyst. Hydrogen which has been chemically converted from fossil fuel or water, methanol which is a liquid or solution in a normal environment, alkali hydride, hydrazine, or dimethyl ether which is a pressurized liquefied gas are used as a fuel, and air or oxygen gas is used as an oxidizing gas.
A fuel is electrochemically oxidized on the anode and oxygen is reduced on the cathode, which generates an electrical potential difference between those two electrodes. If, at this point, an external circuit load is applied between the two electrodes, ion transfer occurs in the electrolyte, and consequently, electrical energy is supplied to the external load.
Of all fuel cells, a direct methanol fuel cell (DMFC) which uses liquid fuel, and metal hydride or hydrazine fuel cells are considered effective as a small and portable or mobile power source because those fuels' volume energy density is high. Especially, the DMFC which utilizes methanol as a fuel is considered an ideal power supply system because methanol is easily handled and is expected in the future to be produced from biomass.
Japanese Laid-open Patent Publication No. 2002-1095, No. 2002-305000 and No. 2003-93874 aim to increase performance of the above-mentioned electrode catalyst.